1. Technical Field of the Invention
The present invention relates to vehicle alternators and, more particularly, to a vehicle alternator having a brush unit formed in a degradation-minimizing structure.
2. Description of the Related Art
With vehicle alternators of the related art, it has been a usual practice to include a rectifier unit and a brush unit disposed along an axis of a rotary shaft in an overlapping relationship. The rectifier unit includes a horseshoe-shaped cooling fan radially extending and fixedly carrying thereon rectifying elements. Under such a structure, the cooling fan has a radially inward end placed in close proximity to an outer periphery of the brush unit.
An attempt has heretofore been made to provide a vehicle alternator structured to have a rectifier unit, fixedly supported on an external surface of a frame, which is covered with an end cover as disclosed in U.S. Pat. No. 6,184,602. The end cover has cooling windows admitting cooling airflows for cooling the rectifier unit.
With an ongoing progress in recent years on development of vehicle alternators each with a minimized structure at an increased power output, an issue arises with the occurrence of a less clearance between a largely sized rectifier unit and a brush unit. However, a cooling fan, reaching a high temperature, provides a radiation heating to the brush unit placed in close proximity to the cooling fan. This causes an increase in temperatures of brushes inside the brush unit. The increase in brush temperatures results in an increase in electrical resistances of the brushes, leading to the occurrence of the brushes being heated. This results in early wears of the brushes while causing a reduction in excitation current. This might be addressed by placing the cooling fin and the brush unit away from each other. However, this results in an increase in a physical size of the vehicle alternator.